1. Technical Field
The present invention generally relates to an energy management system for an energy storage device. More particularly, the present invention is directed to a multiplexed modular battery management system for multi-cell battery packs which may be suitable for electric and hybrid vehicles.
2. Discussion
In order to commercialize electric and hybrid vehicles on a widespread basis, the energy storage devices or batteries which are the most expensive component of the vehicle must operate reliably through the life of the vehicle. To assist in the reliable operation of the battery, a battery energy management system can be utilized.
The commonly used centralized battery energy management systems require the monitoring and controlling of many physical and electrical attributes of the battery, sometimes in as small a battery segment as a single cell. These attributes typically consist of cell voltages, temperatures, state of the charge (SOC), or any derivatives of these attributes, like temperature and voltage variations among the cells. The collection and transmission of this data to a central processor associated with the battery management system for large battery packs involves using a complex network or array of wires and connectors that tend to add cost and complexity to the system.
As an example, consider a centralized battery energy management system for a 48-cell Li-Ion battery pack. To monitor the voltages of all 48 cells, a centralized management system would require 49 lines to the battery pack; consisting of 48 individual battery voltage lines and one battery ground line. Moreover, if the lines have significant length, monitoring and equalization functions controlled by the energy management system cannot share the same lines, and equalization would require another 49 lines since the equalization currents may cause slight voltage drops that corrupt the voltage measurements.
Accordingly, it is desirable to provide a modular battery management system which uses a multiplexed communication system for reducing the number of wiring harness lines within the vehicle. It is also desirable to provide a battery management system in which a plurality of local modules are distributed between the battery pack and a central module. Finally, it is desirable to provide a local module having a simplified and low cost output stage which may be used as an alternative to an isolation amplifier.